1. Field of the Invention
The present invention relates to an information processing apparatus that generates print data for printing by an inkjet printing apparatus, and a control method thereof.
2. Description of the Related Art
Heretofore, a printing system is known in which print data is generated in a host computer such as a personal computer (PC), and the generated print data is output to a printer and printed to a printing medium such as paper by the printer.
Also, a method in a printing system is known that involves compressing print data to be output from the host computer to a printer, and transmitting the compressed print data. As an example, the host computer outputs print data to the printer after reducing the data size thereof by lossily compressing raster image data included in the print data using JPEG encoding or the like. The printer prints the received print data after decompressing the lossily compressed raster image data included in the print data. Print data is transferred from the host computer to the printer at high speed when the data size of the print data is reduced, thereby speeding up the printing process in the printing system.
When image data is lossily compressed using JPEG encoding or the like, the high-frequency component of the image data is lost and image quality deteriorates. Therefore, deterioration in image quality is particularly severe in parts of the image that include a large amount of high-frequency component, such as characters and simple graphics, for example.
In contrast, a technique is known that involves separately rasterizing tonality-oriented image data and resolution-oriented image data, and compressing the former with emphasis on tonality and the latter with emphasis on resolution (see Japanese Patent Laid-Open No. 10-207664).
Many inkjet printers that print by discharging ink are provided with a plurality of inks with different properties, so as to be able to appropriately print various images with different characteristics, such as character images and photo images, to various printing media.
One of the ink properties is permeability to the printing medium. With low permeability ink, a considerable amount of ink remains on the surface of the printing medium. Therefore, advantages include high density and being able to print a sharp image. On the other hand, with low permeability ink, the rate of permeability to the printing medium is slow, increasing the time required for the ink remaining on the surface of the printing medium to fix. As a result, if another ink droplet adheres to an adjacent position, a reaction occurs at the boundary of both inks, causing deterioration in print quality. One such phenomenon is called bleeding, which occurs as a result of differences in permeability between inks or differences in surface tension.
Given the aforementioned advantages, low permeability ink is generally used in printing black characters which require high visibility and vividness. Therefore, there are inkjet printers that have low permeability black pigment ink for printing black characters, and high permeability color dye ink for printing other images.
With such inkjet printers, bleeding occurs at the boundary between the ink droplets of these inks, since both black pigment ink and color dye ink are used on a single printing medium. Particularly, if dye ink contaminates a character printed with pigment ink, the visibility and vividness of the character is greatly reduced, detracting from the advantages of using low permeability ink. Hereinafter, the phenomenon where dye ink contaminates a character printed with pigment ink will be described with reference to FIG. 2.
A raster image 200 has been obtained by an inkjet printer decompressing image data lossily compressed by a host computer. An enlarged image 205 is an enlarged image of part of the raster image 200.
In the enlarged image 205, an area 201 is to be printed using color dye ink. An area 202, which is part of the black character “t”, is to be printed with black pigment ink. The boundary between the character and the background image is normally a high-frequency area, with noise readily occurring when this area is lossily compressed using JPEG encoding or the like. Noise 203 and noise 204 show in simplified form the noise that has occurred.
The noise 203, showing noise that occurs outside the character area (area 202), is an intermediate color between black and the background color. Such noise 203, not normally being completely black, is printed using color dye ink during printing. Therefore, deterioration in print quality due to bleeding does not readily occur in the area 201 printed with high permeability color dye ink, because the same color dye ink is used in printing, despite being printed as noise.
On the other hand, the noise 204 that occurs inside the character area (area 202), similarly not being completely black, is printed with color dye ink. That is, the noise 204 is printed with high permeability color dye ink inside the area 202 printed with low permeability black pigment ink. As a result, there will be patches printed with inks of differing permeability in a small area (area 202, noise 204), causing severe deterioration in print quality due to bleeding. Specifically, the black pigment ink blurs around the outline of the character, and the character outline loses its vividness.
Deterioration in print quality due to raster image data being lossily compressed is thus closely related to the properties of the inks used during printing. In other words, the effect on print quality differs greatly depending on the properties of the inks used during printing, even with comparable noise produced by lossy conversion.
However, while conventional techniques such as Japanese Patent Laid-Open No. 10-207664 take into consideration mitigating noise that generally occurs readily during lossy conversion, deterioration in print quality with the use of inks having different properties is not taken into consideration.